1. Field of the Invention
The present invention relates to an antenna which is provided in a portable radio, represented primarily by devices for mobile communication terminal such as a portable telephone, PHS (Personal Handy Phone System), and the like. In particular, this invention relates to the antenna for portable radio which is installed to a case of the portable radio and can be freely extracted and stored therefrom/therein.
2. Description of the Related Art
An antenna which can be extracted during use, and stored inside the case of the radio when not in use, is used in this type of portable radio. Such a storable antenna comprises (a) a rod antenna section having a predetermined wavelength (one-quarter, three-eighths, one-half, etc.) when extracted from the radio case, and (b) a coil antenna section which is provided in an insulated state at the tip of the rod antenna section, and has a predetermined wavelength when projected from the radio case while the rod antenna is being stored. A feeding mechanism is provided at the antenna installation position on the radio case. The feeding mechanism electrically connects to the bottom end of the rod antenna section when the rod antenna is extracted, and electrically connects to the bottom end of the coil antenna section when the rod antenna is stored.
A conventional example of the feeding mechanism described above will be explained based on FIGS. 8 and 9. Firstly, the basic constitution of the antenna will be explained based on FIG. 8. As already explained, an antenna 1 comprises a coil antenna section 10 and a rod antenna section 20. A sleeve 12 of conductive material is provided as a feeding member at the base of the coil antenna section 10, which is provided at the tip of the antenna 1. A stopper 22 of conductive material is provided at the base of the antenna as a feeding member of the rod antenna section 20, which connects to the base of the sleeve 12. The coil antenna section 10 is provided at the tip of the antenna 1, and comprises a coil element 14 which is wound around a cylindrical bobbin 13 provided inside a top 11. The coil element 14 is electrically connected to the sleeve 12, which is coupled to the base of the top 11. The rod antenna section 20 comprises a flexible antenna tube 21 having elasticity which covers an antenna element 23. The antenna element 23 connects to the base of the stopper 22, provided at the base of the antenna.
When manufacturing the antenna 1, a holder 30 is attached while the stopper 22 is in the fastened state. The holder 30 comprises a conductive member. A screw section 30a is provided around the outer rim of the holder 30, and a groove 30b for a screw-stopping fitting is provided in a flange-like head section. A holding spring 31 is provided inside the holder 30, and maintains electrical contact with the stopper 22 and the sleeve 12. FIG. 9 shows the state when the antenna 1 is attached to the radio case 2 by the holder 30. An installation metal fitting 32 has a screw section in its inner rim, and is provided at the antenna installation position on the case 2. The screw section 30a around the holder 30 screws into the screw section in the installation metal fitting 32. A special fitting 40, such as that shown in FIG. 10, is inserted into the groove 30b at the head of the holder 30 and clamping is carried out. A feeding spring 33 is connected to the installation metal fitting 32, and electricity is supplied via the feeding spring 33 to a radio circuit board comprising an RF substrate 4. A storage cylinder 34 is provided below the installation metal fitting 32.
The conventional feeding mechanism in the antenna 1 described above has the following problems. Firstly, electrical contact resistance is high and signal transmission is unstable. According to the constitution described above, a received signal flows from the coil antenna and the rod antenna element 14 and 23, via the sleeve 12 or the stopper 22, the holding spring 31, the holder 30, the installation metal fitting 32, and the feeding spring 33, to the RF (Radio Frequency) substrate 4. Transmitted signals flow along the same route in reverse, passing from the RF substrate 4, via the feeding spring 33, the installation metal fitting 32, the holder 30, the holding spring 31, the sleeve 12 and the stopper 22, to the coil antenna and the rod antenna element 14 and 23. There are a great many contact points between the members which signals pass through during transmission, and consequently the electrical contact resistance becomes as high as 200 mxcexa9 to 1 xcexa9. Furthermore, noise is liable to enter the signals at the contact points between the members during transmission, making signal transmission unstable.
Secondly, there is a serious problem regarding weight. Since portable radios such as mobile telephones and PHS, are often carried in users"" pockets and the like, the total weight of the portable radio needs to be extremely light. However, in the conventional constitution described above, the weight of the main body of the antenna 1 (including the holder 30) with the addition of the installation metal fitting 32 is approximately 2.3 g. This is an impediment to making the portable radio lighter.
Thirdly, there is a problem of workability when attaching the antenna 1 to the radio case 2. In the above constitution, in attaching the antenna 1 to the radio, the holder 30 must be screwed to the installation metal fitting 32 of the radio. As shown in FIG. 10, this screwing operation requires the special fitting 40. In addition, the torque of the clamping must be controlled, making this operation bothersome. Furthermore, there is a possibility that the groove 30b for joining the fitting will be damaged during the screwing operation. Moreover, the presence of the groove 30b for joining the fitting leads to a problem that the antenna tube 21 of the rod antenna section might be damaged by touching the edges of the groove.
Fourthly, there is a problem of variation in the sliding forces of the holding spring 31 and the sleeve 12 or the stopper 22. In the conventional mechanism, the holding spring 31 must be provided in a small limited space inside the holder 30. As a consequence, the holding spring 31 has a short contact piece length and little flexion. This results in an unstable sliding force between the holding spring 31 and the sleeve 12 (stopper 22), the sliding force varying between approximately 200 to 600 g.
Fifthly, the conventional feeding mechanism comprises so many components that the cost of the antenna 1 is high.
The present invention has been achieved in order to solve the above problems. It is an object of this invention to improve the feeding mechanism of the antenna by reducing the contact resistance, stabilizing signal transmission, reducing the weight of the antenna, simplifying the operation of installing the antenna, upholding product quality, and reducing costs.
In order to achieve the above objects, a first aspect of this invention provides an antenna for portable radio comprising an antenna section which functions when extracted from a case of a portable radio, and a stopper which comprises a feeding member and is provided at the base of the antenna section. The antenna can be freely extracted from and stored in the case. A cylindrical section is provided on the case at the antenna installation position, and the stopper reaches a clipped state after being inserted into the cylindrical section. The cylindrical section comprises a plate-like feeding spring which pressingly contacts one end of the feeding member when the feeding member faces inside the cylindrical section. The plate-like feeding spring holds the antenna section and feeds electricity when the antenna section is extracted.
A second aspect of this invention provides the antenna for portable radio of the first aspect, wherein the other end of the plate-like feeding spring connects to another element.
A third aspect of this invention provides the antenna for portable radio of the first aspect, wherein a slit is provided in the stopper so that the diameter of the stopper decreases during insertion into the cylindrical section and the stopper reaches a clipped state after insertion.
A fourth aspect of this invention provides the antenna for portable radio of the first aspect, wherein the stopper comprises an attachment section which a clipping member is attached to after insertion into the cylindrical section.
According to the above constitution, the antenna can be installed to the radio case without using a holder. A cylindrical section is provided at the position on the radio case where the antenna is installed, and, after the stopper of the antenna has been inserted into the cylindrical section, the stopper becomes securely clipped therein. Specifically, the stopper comprises a slit which allows the diameter of the stopper to be reduced during insertion into the cylindrical section. After the stopper has been inserted, the slit elastically opens, securely clipping the stopper. Alternatively, a clipping member may be provided for clipping the stopper in position after it has been inserted into the cylindrical section. Therefore, during normal use, the antenna is fastened to the cylindrical section so as to prevent from falling off and can slide in and out normally. When removing the antenna in the case of a malfunction or the like, the antenna can be pulled out of the cylindrical section by a force which is greater than a predetermined force (e.g. 10 kg.f).
According to the feeding mechanism of this constitution, the cylindrical section comprises a plate-like feeding spring. When the stopper or the sleeve faces the cylindrical section, one end of the plate-like feeding spring pressingly contacts the stopper or the sleeve. The other end of the plate-like feeding spring directly pressingly contacts the circuit substrate connection point of the radio.
According to this constitution, the holder of the conventional example is removed and the stopper of the antenna is directly attached to the side of the case. Therefore, the complexity of affixing the holder by screwing can be eliminated. In addition, damage to the antenna tube caused by a fitting groove of the holder can be eliminated. The feeding mechanism comprises a plate-like feeding spring which jointly provides the functions of the conventional holding spring and feeding spring, and feeds electricity from the feeding member of the antenna, via the plate-like feeding spring, and directly to the circuit substrate. Therefore, the feeding mechanism has few electrically contacting parts, reducing the contact resistance and contact noise, thereby stabilizing signal transmission. Further, since there are few restrictions on space, the feeding member of the antenna can have a sufficient contact piece length. Consequently, the pressing contact force of the spring can be stabilized, enabling a stable sliding force to be applied to the stopper and the sleeve inside the cylindrical section.
Further, this invention comprises fewer components at the attachment point of the antenna and the radio case, and in the feeding mechanism, than the conventional example. Therefore, the cost and weight can be reduced.